Lec Ch 03 Water and Life SB

Why is water a polar molecule?

Electrons spend more time near oxygen than hydrogen, giving water an uneven charge distribution

What allows water molecules to form hydrogen bonds with each other?

Polarity of water

What are the four emergent properties of water that support life?

Cohesive behavior, ability to moderate temperature, expansion upon freezing, versatility as a solvent

What is cohesion?

Hydrogen bonds holding water molecules together

What is surface tension?

Measure of how difficult it is to stretch or break the surface of a liquid

Why is cohesion important in plants?

Helps transport water and nutrients against gravity

What is adhesion?

Attraction between different substances, such as water and plant cell walls

How does adhesion help plants?

Counters the downward pull of gravity in water transport

What is kinetic energy?

Energy of motion

What is thermal energy?

Kinetic energy associated with random motion of atoms or molecules

What is temperature?

Measure of the average kinetic energy of molecules in a substance

What is heat?

Thermal energy transferred from one body to another

What is a calorie (cal)?

Heat required to raise 1 g of water by 1°C, or released when it cools by 1°C

What is a kilocalorie (kcal)?

1,000 calories; unit used in food energy

What is a joule (J)?

Energy unit; 1 J = 0.239 cal, 1 cal = 4.184 J

What is specific heat?

Amount of heat needed to change 1 g of a substance by 1°C

What is the specific heat of water?

1 cal/(g·°C)

Why does water resist temperature change?

High specific heat due to hydrogen bonding

What happens when hydrogen bonds break?

Heat is absorbed

What happens when hydrogen bonds form?

Heat is released

Why is water’s high specific heat important?

Minimizes temperature fluctuations, stabilizing environments

How do large bodies of water moderate climate?

Absorb heat in summer, release heat in winter

What is evaporation (vaporization)?

Transformation of a liquid into a gas

What is heat of vaporization?

Heat required for 1 g of liquid to become gas

What is evaporative cooling?

Cooling that occurs because the hottest molecules evaporate first

Why is evaporative cooling important?

Stabilizes temperatures of organisms and ecosystems

Why is ice less dense than liquid water?

Hydrogen bonds hold molecules apart in a crystalline lattice

At what temperature is water most dense?

4°C

Why does ice float?

It is about 10% less dense than liquid water

Why is floating ice important for life?

Insulates bodies of water, preventing them from freezing solid

What is a solution?

Homogeneous mixture of substances

What is a solvent?

Dissolving agent in a solution

What is a solute?

Substance that is dissolved

What is an aqueous solution?

Solution where water is the solvent

What is a hydration shell?

Sphere of water molecules surrounding dissolved ions

Can water dissolve nonionic polar molecules?

Yes, because of its polarity

Can proteins dissolve in water?

Yes, if they have polar or ionic regions

What is a hydrophilic substance?

One that has an affinity for water

What is a hydrophobic substance?

One that repels water, often nonpolar (like oils)

Why are hydrophobic molecules important in cells?

They are major components of membranes

What is molecular mass?

Sum of all atom masses in a molecule

What is a mole (mol)?

6.02 × 10²³ molecules (Avogadro’s number)

What is molarity (M)?

Moles of solute per liter of solution

Why do biologists look for water on other planets?

Water is critical for life as we know it

What happens during water dissociation?

A hydrogen atom shifts, forming H⁺ and OH⁻ ions

What is a hydroxide ion (OH⁻)?

Water molecule that lost a proton

What is a hydronium ion (H₃O⁺)?

Water molecule that gained a proton

What is pH?

Negative logarithm of hydrogen ion concentration: pH = –log[H⁺]

What is the pH of pure water?

7 (neutral)

What is an acid?

Substance that increases H⁺ concentration

What is a base?

Substance that decreases H⁺ concentration

What is a strong acid or base?

One that dissociates completely in water

What is a weak acid or base?

Reversibly releases or accepts hydrogen ions

What pH values indicate acidic solutions?

Less than 7

What pH values indicate basic solutions?

Greater than 7

What is the typical pH range of biological fluids?

6–8

What is a buffer?

Substance that minimizes changes in H⁺ and OH⁻ concentrations

How do buffers usually work?

Contain weak acid-base pairs that reversibly bind H⁺ ions

Why is buffering important in cells?

Even slight pH changes can harm living systems

What is ocean acidification?

CO₂ dissolves in seawater, forming carbonic acid

How does ocean acidification affect carbonate ions?

Reduces carbonate concentration by forming bicarbonate